EP1930687A1 - Store for measurement machine and corresponding tool - Google Patents

Abstract

The rack (20) has a housing for storing a set of interchangeable tools (200). The housing has guides (60) for allowing the interchangeable tools to be inserted into a free space of the housing between the guides along a direction. The housing has retaining surfaces for limiting the movements of the tools in another direction. A tooth (100) is provided between the guides for limiting the movements of the tools in the latter direction in a plane other than that of the retaining surfaces and the guides, to tilt the tools when a force is applied to the tools along the latter direction. An independent claim is also included for a method for actuating a coordinate measuring machine.

Description

Technical area

The present invention relates to a system of tools connectable to a coordinate measuring machine, for example a touch probe, a video camera or any other mechanical or optical measuring tool that preferably sends electrical signals, and a magazine allowing the automatic exchange of tools during a measuring operation with the machine and a corresponding tool. The present invention is not limited to the field of metrology or measurement of dimensions, but can be applied to robots with interchangeable tools, or to any other system having automatically interchangeable tools.

State of the art

Several examples of coordinate measuring machines with automatically interchangeable tools are already known. These are, in general, measuring systems in which the moving head of the measuring machine and the tools comprise mutual coupling devices, which can be locked and unlocked automatically, and able to achieve a very precise and stable mechanical connection between the measuring head of the machine and the chosen tool.

Known systems also often include tool magazines, placed in the work volume of the measuring machine, in which the machine can set the tools at the end of a measurement task, and take the tool required for the measurement. next task. The measuring machine can thus perform complex series of measurements, following a sequence of programmed movements, or following the manual commands of an operator.

The precision of the coupling between the measuring head and the various tools is obviously essential for the accuracy of the measurements. It is also very important that this coupling is highly reproducible, to avoid calibration operations with each tool change. For this purpose, an isostatic connection is often provided with exactly six points of contact between the measuring head and the tool, so as to determine exactly the positioning of the tool relative to the measuring head. The patent application EP1577050 describes a connection with three pins whose axes are spaced apart by 120 ° on the measuring head, and three pairs of balls positioned in correspondence on the tool, making an isostatic connection.

In this type of connection, precision is based on the quality of the contact surfaces. It is therefore important, during connection and disconnection operations, to avoid or limit shocks that can modify or alter these surfaces.

The document US4651405 describes measuring tools, intended to be connected to the arm of a coordinate measuring machine by a mechanical connection, using an appendage on the tool which engages with a cam of the measuring head. Locking of the tool on the machine takes place when the cam is turned 90 ° by another tool provided for this purpose. If it is desired to automate this operation, the tool magazine must contain one or more actuators to actuate the cam and move from the locked position to the unlocked position, and vice versa, as required.

These devices comprise, for each position of the magazine, an actuator to actuate the cam and lock, respectively unlock the tool. These actuators, and the associated control devices, increase the complexity and cost of the store, and require described cam systems.

The patent application EP416524 discloses a feeler and a tool magazine with a magnetic connection between the head and the feeler key, comprising a permanent magnet and an electromagnet. When changing the tool, the magnetic force can be neutralized by an electromagnet in the measuring head, thus allowing the separation between measuring head and tool. The patent US5028901 describes a similar system, wherein the electromagnet is external and separate from the measuring head.

A limitation of these known systems is that they require an additional element, which increases the cost, complexity and dimensions of the measuring head.

The patent EP426492 describes an interchangeable probing key linked by magnets to the probe body. This key has no elements intended to interface with an automatic tool change system.

The patent US4604787 describes an industrial robot arm with interchangeable tools, able to drop a tool into a magazine slot and grab a new tool from the same shop. The magazine has slots for the tools, in which the tools can be slid in a direction transverse to their axis, and are retained axially. The mechanical connection between the arm and the tool opens automatically under the effect of an axial separation force exceeding a predetermined threshold.

The patent EP566719 discloses a tool system and a magazine in which the tools comprise a permanent magnet and are magnetically retained on the corresponding measuring head. The separation between the tool in the magazine and the measuring head takes place under the action of an axial pulling force exceeding the magnetic attraction, analogically to that described in the document US4604787 .

In these systems, the axial force required to pull the tool is quite large, and this poses problems in achieving high accuracy. It is important, for the accuracy of the measuring system, that the magazine, the tool and the arm of the measuring machine do not undergo excessively high mechanical forces, which may lead to inaccurate adjustment and inaccuracy.

Brief summary of the invention

An object of the present invention is to provide an interchangeable tool and a corresponding magazine free from the limitations of known devices.

The invention also proposes the object of increasing the precision and the reproducibility of the tool change operation.

This object is achieved by the devices which are the subject of the independent claims, optional features being introduced in the dependent claims and in the description.

Brief description of the drawings

• La figure 1 illustre un magasin d'outils avec des logements pour plusieurs outils selon un mode de réalisation de l'invention.
• La figure 2 illustre le magasin d'outils de la figure 1 avec un logement occupé par un outil, en ce cas un palpeur pour une machine à mesurer des coordonnées.
• La figure 3 illustre le magasin de l'invention en une position repliée, selon un aspect de l'invention.
• La figure 4 montre en détail deux logements du magasin d'outils de l'invention, vus du haut en représentation isométrique.
• La figure 5 montre en détail deux logements du magasin d'outils de l'invention, vus du bas en représentation isométrique.
• La figure 6 illustre la position de l'outil dans le magasin suite à la déconnexion de l'outil de la tête de mesure.

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

• The figure 1 illustrates a tool magazine with housings for several tools according to one embodiment of the invention.
• The figure 2 illustrates the tool store the figure 1 with a housing occupied by a tool, in this case a probe for a machine to measure coordinates.
• The figure 3 illustrates the store of the invention in a folded position, according to one aspect of the invention.
• The figure 4 shows in detail two housings of the tool magazine of the invention, seen from above in isometric representation.
• The figure 5 shows in detail two housings of the tool magazine of the invention, seen from the bottom in isometric representation.
• The figure 6 illustrates the position of the tool in the magazine following the disconnection of the tool from the measuring head.

Example (s) of embodiment of the invention

The figure 1 illustrates a tool magazine 20, specially designed to house interchangeable tools 200 of a coordinate measuring machine (CMM), and the following description refers to this particular application. The invention, however, is not limited to this application, but can also be applied to magazines for automatic machine tools, industrial robots, or any other interchangeable tool machine.

The magazine 20 includes a base 85 for attachment in the operation volume of the CMM. Typically the base 85 is securely fixed on the reference plane of the machine (not visible), on which also rest the pieces to be measured. Other arrangements are possible, however. The position of the magazine 20 in the repository of the machine to be measured is determined prior to the measurement and the tool change, for example by the coordinates of a series of predefined reference points, recorded during a calibration procedure. well known to those skilled in the art.

In the remainder of the description reference will be made to the vertical direction as being the direction perpendicular to the reference plane of the measuring machine, which is conventionally a horizontal reference plane. These references to conventional orientations are intended only to improve the readability of the description and do not limit the invention, which could be applied to tool magazines oriented in any direction in space. The terms "high" and "low", "higher" and "lower" should also be interpreted as descriptive and non-limiting terms relating to these conventional orientations.

The magazine 20 preferably comprises a plurality of housings, for storing a plurality of tools 200. In this way, it is It is possible to carry out complex measurements employing various tools, the CMM being arranged to deposit a tool in an available housing of the magazine 20, and then to take another tool in another housing, whenever it is necessary. Advantageously, and with reference to figure 2 , the housings are carried by an upper body 650, raised relative to the base 85 by the arm 83, so as to accommodate tools of different heights without fear of contact with the reference surface.

Referring now to the figure 3 , the arm 83 is preferably articulated, along the axes 81 and 82, so as to fold in case of collision. In this way, the risk of damage is reduced, for example due to mishandling on the measuring machine, causing a shock between the measuring head, the measuring tool and the magazine. In normal condition, the magazine 20 is held in the unfolded position of the figure 2 by precise elastic expansion devices of known type, not shown. Shocks, also not visible in the figure, dampen the withdrawal of the store, in case of shock.

Preferably each housing comprises a protective cover 50, visible in detail on the figure 4 , capable of sliding in a horizontal direction, between an open position in which the corresponding housing is accessible, and a closed position, protecting the housing and any tool therein. The protections 50 may also, alternatively, lock in the open position.

Each housing also includes guides 60 for inserting the tools in the housing in a horizontal direction and removal of the housing tools in the same direction. According to the variant of the invention represented by the figure 1 and, in more detail, by the figure 5 , the magazine 20 comprises a body 650, resting on the arm 83 and on which the protective covers 50 slide. The guides 60 consist of two straight and parallel ridges cut in a metal plate 630 screwed or fixed on the body 650.

The tool 200 comprises surfaces or zones of engagement 210, cooperating with the guides 60. In the example shown ( Fig. 1 ) the engagement surfaces are surfaces of an annular groove of square or rectangular section 210 symmetrically surrounding the circular body of the tool 200. However, other arrangements are possible.

The connection between the tools and the measuring machine is effected by means of an adapter 300 fixed to the moving head of the measuring machine. In the example shown ( Fig. 1 ) the adapter is attached to the movable head (not visible) by a threaded rod 330. Other fastening systems are however possible and included in the present invention. Preferably the tool 200 and the adapter 300 are precisely and reproducibly connected by magnetic elements 260, for example permanent magnets, and by a system of precision contact members, for example three pins whose axes are spaced apart. 120 ° on the measuring head, and three pairs of balls positioned in correspondence on the tool, making an isostatic connection, determining exactly the positioning of the tool relative to the measuring head.

In the illustrated case of a screwable adapter, an annular, or at least axially axial, engagement surface 210 is particularly suitable. It is actually difficult to ensure a given angular position of the adapter on the head, because it depends on the clamping force and the friction between the surfaces. The annular groove 210 has no preferred orientation and can perform its function, as will be explained later, regardless of the angle or relative positioning of the tool relative to a vertical axis.

When a tool is deposited in the magazine, the measuring machine moves its measurement head, with the adapter 300 and the tool 200, in front of a housing of the magazine 30, the groove 210 aligned with the guides 60. The measuring head then moves horizontally, in a direction parallel to the guides 60, until the guides 60 engage in the groove 210. The internal diameter of the groove 210 corresponds to the distance between the guides 60, with sufficient clearance, for example a game of some tenth of a millimeter, to consent easy insertion and without lateral constraints.

The cover 50, if present, is normally held in the closed position by a spring or other suitable elastic element. When moving horizontally mentioned above. Adapter 300 contacts the cover and slides to access the magazine housing.

With reference to the figure 4 each housing has a tooth 100 between the guides 60. The insertion of the tool 200 between the guides 60 ends when the tooth 100 engages, at least partially, in the groove 210. According to one aspect of the In the invention, the lower surface 120 of the tooth 100 is not aligned on the horizontal plane of the lower surfaces 110 of the guides 60. For example, the lower surface 120 of the tooth 100 is offset downwards by 0.10-0.50. mm with respect to the plane of the lower surfaces 110 of the guides 60.

1. 1. puisque la force de la liaison magnétique et la force appliquée par la dent 100 ne sont pas alignées, une séparation apparaît entre l'adaptateur 300 et l'outil 200. Ce dernier bascule d'un angle α (voir figure 6) jusqu'à que la gorge 210 de l'outil entre en contact avec les surfaces inférieures 110 des guides 60. Grâce à l'effet de levier, la force appliquée par la dent 100 est sensiblement inférieure à la force totale d'attraction magnétique.
2. 2. le basculement fait augmenter l'entrefer entre les éléments magnétiques sur l'outil 200 et l'adaptateur 300. La force magnétique dépend très sensiblement de l'entrefer, le basculement entraîne une réduction appréciable de la force d'attraction. Et prédispose le décrochage de l'outil.

The disconnection of the tool 200 from the adapter 300 is carried out as follows: the measuring machine is actuated so as to cause a vertical movement of the measurement head upwards. During this movement the lower surface 120 of the tooth 100 (see figure 5 ) comes into contact with the inner lower surface of the groove 210. From this moment, the tool can no longer follow the vertical movement of the adapter, because it is retained by the retaining surface 120 of the tooth 100. Two effects then occur:

1. 1. since the force of the magnetic link and the force applied by the tooth 100 are not aligned, a separation appears between the adapter 300 and the tool 200. The latter switches from an angle α (see figure 6 ) until the groove 210 of the tool comes into contact with the lower surfaces 110 of the guides 60. Thanks to the lever effect, the force applied by the tooth 100 is substantially less than the total force of magnetic attraction .
2. 2. tilting increases the air gap between the magnetic elements on the tool 200 and the adapter 300. The magnetic force depends very substantially on the air gap, the tilting causes an appreciable reduction in the force of attraction. And predisposes the stall of the tool.

Tilting is limited by the lower support surfaces 110 (see FIG. figure 5 ) guides 60 coming into contact with the lower surface of the groove 210. From this moment the vertical force exerted by the magazine 20 on the tool 200 is shared between the two lower retaining surfaces 110 of the guides 60 and the lower surface retaining 120 of the tooth 100. When this force exceeds the magnetic attraction, reduced following the tilting, there is complete separation of the tool 200 of the adapter 300.

The arrangement of the invention makes it possible to appreciably reduce the mechanical forces exerted on the guides 60 during the uncoupling. This reduction is due to the tilting of the tool and to the fact that the residual retaining force due to the magnetic effect is shared between the two lower retaining surfaces 110 of the guides 60 and the lower retaining surface 120 of the tooth 100. This sharing of force over three points or regions of contact has a positive effect on mating accuracy.

For example, a lower offset of the surfaces between the tooth 100 and the lower retaining surfaces of the guides 60 by 0.25 mm is sufficient to cause a tilting angle of about 2 °, which is very effective.

The leaf springs 150 (see figures 1 and 4 ) rest on the upper surface of the groove 120, introducing a certain friction, in order to avoid any unwanted movement of the tool in the housing, for example following vibrations, without, however, completely blocking the tool 200 and cause significant effort on the head when changing tool. In this way, when the tool is taken again, the measuring head can find it exactly in the same position and in the same orientation to which it was left when the disconnection. According to one variant, the leaf springs 150 could be replaced by one or more permanent magnets or magnetic elements in the magazine 20.

To load another tool, the measuring machine is actuated to center above the known position of a tool in a chosen housing, possibly by moving the cover 50, if present. The head is then moved vertically downward until the tool 200 is connected to the adapter 300 and until the groove 210 is no longer in contact with the lower tooth holding surface 100 or those Finally, the head moves horizontally, in the direction defined by the guides 60, until complete release of the tool 200 from the magazine 20.

Accurate and reproducible coupling of the tool 200 critically depends on the position of the latter in the magazine 20. It is important, in particular, that the tool rests in its housing exactly in the same position and in the same orientation to the measuring machine left it, and this with a minimum of mechanical constraints. In this way the coupling can take place precisely. Preferably the springs 150 leave a slight mobility to the tool for the coupling operation, allowing the isostatic means to position themselves precisely. The improper positioning of the tool 200 or the magazine 20 on a CMM machine can cause shocks during reconnection which are detrimental to the accuracy of the calibration and measurement, and irreversibly alter the contact surfaces.

In order to ensure the stability of the tool 200 on the adapter 300, even in a dynamic displacement condition, the magnetic attraction force between these two elements is generally quite large, of the order of 1 kgf or more, for avoid the loss of the tool while the machine is working. It is difficult to pull the tool 200 from the adapter 300 from a only once, without introducing displacements or undesirable vibrations during the uncoupling. The device of the invention makes it possible to carry out this separation gradually and without these defects, this by distributing the mechanical forces on three retaining surfaces, reducing the magnetic attraction force by the tilting of the tool, and orienting the tool for the stall avoiding a random stall as is the case when the tool is not inclined preferentially.

Advantageously, the device of the invention ensures that the contacts and separations of the contact members between the tool 200 and the adapter 300 are always succeeding in the same order, during the hooking and unhooking. This appreciably improves the accuracy and reproducibility of the coupling.

The tool magazine 20 of the invention furthermore has the advantage that the disconnection and connection of the tools are performed solely by passive elements and the movements of the measuring machine, without resorting to additional actuators for locking or unlock the tool.

Claims (18)

A magazine (20) for storing one or more tools (200) of a coordinate measuring machine, each tool (200) being detachably connectable to the movable arm of the coordinate measuring machine, with at least one housing for storing a tool (200), said at least one housing comprises: guides (60) for inserting the tools (200) into the housing in a first direction and removing the tools (200) from the housing in the first direction; retaining surfaces (120, 110) for limiting movement of the tool in a second direction, characterized in that
the guides (60) and the retaining surfaces (120, 110) are arranged to cause a tilting of the tool (200). Magazine (20) according to the preceding claim, wherein the tilting of the tool occurs when a force is applied to the tool in the second direction. Magazine (20) according to one of the preceding claims, wherein the retaining surfaces (120, 110) lie on at least two distinct planes orthogonal to the second direction. Magazine (20) according to one of the preceding claims wherein at least one housing comprises two guides (60) substantially rectilinear and parallel to the first direction and separated by a free space, allowing insertion of the tools (200) in the free space between the guides (60), wherein the guides (60) also comprise retaining surfaces (110) lying in a plane substantially orthogonal to the second direction and limiting the movements of the tool in the second direction; at least one housing further comprising a tooth (100), between the guides, limiting the movements of the tool in the second direction, in a plane other than the retaining surfaces than the guides (60) to cause a tilting of the tool when a force is applied to the tool in the second direction. Store according to one of the preceding claims, comprising retention means (150) for moderating the movements of the tool, without, however, prohibiting them completely. Magazine according to one of the preceding claims, comprising retention means (150) for holding the tool in the position and orientation in which it has been deposited. Magazine according to one of the preceding claims, comprising retention means (150), which leaves a slight mobility to the tool for the coupling operation, allowing the isostatic means to position themselves precisely. Magazine according to the preceding claim, wherein the retention means (150), for example leaf springs or magnetic elements, introduce a friction between the tool and the guides (60), when the tool moves in the first direction. The combination of a magazine (20) according to one of the preceding claims and a tool (200) detachably connectable to the movable arm of the coordinate measuring machine, wherein the tool (200) comprises engagement zones (210), able to collaborate with the guides (60) and the retaining surfaces (110, 120) of the at least one housing. Combination according to the preceding claim, wherein the engagement zones (210) of the tool (200) are symmetrical relative to an axis of symmetry, and in which, when the tool (200) is inserted into the housing of the store the axis of symmetry is parallel to the second direction. Combination according to one of claims 9-10, wherein the connection between the tool (200) and the movable arm of the measuring machine is magnetic. Combination according to one of claims 9-11, wherein the connection between the tool (200) and the movable arm of the measuring machine is performed by an adapter (300) adapted to cooperate with the tool (200) fixed on the moving arm of the measuring machine. Combination according to one of claims 9-12, wherein the connection force between the tool (200) and the movable arm or the adapter is reduced by the tilting of the tool (200). A method for operating a coordinate measuring machine having a movable arm including connecting means for exchanging interchangeable tools (200), a tool magazine (20) being present in the access range of the movable arm, the magazine having at least one housing for storing a tool (200), the method comprising the steps of: moving the movable arm in a first direction to engage a tool (200) connected to the movable arm in a magazine housing; moving the movable arm away from the magazine in a second direction to detach the tool (200) from the movable arm; wherein, during the removal of the movable arm from the magazine, the retaining surfaces (110, 120) of the housing limit the movements of the tool in the second direction and exert on the tool a force opposite to that exerted by the means. connection, and a tilting torque, to tilt the tool (200) and reduce the force exerted on the tool by the connecting means. Method according to the preceding claim, wherein the connection between the tool (200) and the movable arm of the measuring machine is magnetic. Method according to one of claims 14-15, wherein the tool (200) and the movable arm are accurately and reproducibly linked by an isostatic connection with a plurality of contact members, determining exactly the positioning of the tool (300 ) relative to the movable arm, and wherein the contacts and the separations of the contact members of the isostatic connection are always succeeding in the same order, during the hooking and unhitching. Method according to the preceding claims, wherein the tool (200) is inclined in a preferred direction through the tooth (100), avoiding unsymmetrical sliding between the guides (60) during the recess. Method according to the preceding claims, wherein the tool is positioned in the housing (30) so as not to come into complete contact with the guides, and thus maintain a slight mobility.

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